Substrate sterilization with thiophanate-methyl and its biodegradation to carbendazim in oyster mushroom (Pleurotus ostreatus var. florida)

Residue analysis to detect thiophanate-methyl and its primary metabolite (carbendazim) during oyster mushroom (Pleurotus ostreatus var. florida) cultivation was done for two consecutive years 2017 and 2018. Wheat straw substrate was chemically treated with different treatments of thiophate-methyl, viz, thiophanate-methyl 30 ppm + formalin 500 ppm (T1), thiophanate-methyl 40 ppm + formalin 500 ppm (T2), thiophanate-methyl 50 ppm + formalin 500 ppm (T3), thiophanate-methyl 60 ppm + formalin 500 ppm (T4), and formalin 500 ppm (T5 as control and recommended concentration), and utilized for cultivation of oyster mushroom. Treatments T3 and T4 exhibited significant difference in pH levels during both the trials. Minimum spawn run, pinhead formation, and fruit body formation time were recorded in treatments T3 and T4. Significantly higher biological efficiency (%) was recorded in treatments T3 and T4 as compared with all other treatments. No incidence of competitor molds was recorded in T3 and T4. Pesticide residue analysis for detection of thiophanate-methyl and its metabolite (carbendazim) was done in the fruit body produced in T3 and T4 treatments using liquid chromatography with tandem mass spectrometry method. No residue of thiophanate-methyl and carbendazim was detected at 50 ppm concentration of thiophanate-methyl during both the trials. However, in trial II, residue of carbendazim (5.39 μg/kg) was detected at 60 ppm. Based on the findings of the trials I and II, T3 (thiophanate-methyl 50 ppm + formalin 500 ppm) may be utilized for substrate sterilization for oyster mushroom cultivation and Pleurotus ostreatus var. florida could be recognized as microorganism which could play a role in degradation of thiophanate-methyl.